4,921 research outputs found
Dichloromethylation of enones by carbon nitride photocatalysis
Small organic radicals are ubiquitous intermediates in photocatalysis and are used in organic synthesis to install functional groups and to tune electronic properties and pharmacokinetic parameters of the final molecule. Development of new methods to generate small organic radicals with added functionality can further extend the utility of photocatalysis for synthetic needs. Herein, we present a method to generate dichloromethyl radicals from chloroform using a heterogeneous potassium poly(heptazine imide) (K-PHI) photocatalyst under visible light irradiation for C1-extension of the enone backbone. The method is applied on 15 enones, with Îł,Îł-dichloroketones yields of 18â89%. Due to negative zeta-potential (â40âmV) and small particle size (100ânm) K-PHI suspension is used in quasi-homogeneous flow-photoreactor increasing the productivity by 19 times compared to the batch approach. The resulting Îł,Îł-dichloroketones, are used as bifunctional building blocks to access value-added organic compounds such as substituted furans and pyrroles
Energy and Structure of Hard-Sphere Bose Gases in three and two dimensions
The energy and structure of dilute gases of hard spheres in three dimensions
is discussed, together with some aspects of the corresponding 2D systems. A
variational approach in the framework of the Hypernetted Chain Equations (HNC)
is used starting from a Jastrow wavefunction that is optimized to produce the
best two--body correlation factor with the appropriate long range. Relevant
quantities describing static properties of the system are studied as a function
of the gas parameter where , and are the density,
--wave scattering length of the potential and dimensionality of the space,
respectively. The occurrence of a maximum in the radial distribution function
and in the momentum distribution is a natural effect of the correlations when
increases. Some aspects of the asymptotic behavior of the functions
characterizing the structure of the systems are also investigated.Comment: Proceedings of the QFS2004 conference in Trento. To appear in JLT
Gating of L-type Ca2+ channels in embryonic chick ventricle cells: dependence on voltage, current and channel density
1. L-type calcium channels in embryonic chick heart ventricle have voltage-dependent, time-variant kinetics when they conduct inward currents carried by 20 mM-Ba2+. Depolarizing the membrane from -20 to 20 mV increases mean open time from 1.4 to 4.2 ms. Mean open time increases monotonically with voltage. The single-channel conductance, 18 +/- 2 pS, is approximately linear over this voltage range, and the extrapolated reversal potential is 38 +/- 5 mV. 2. In cell-attached patches with five or more L-type Ca2+ channels in the patch, the currents elicited by 500 ms depolarizing steps, from a -80 mV holding potential, inactivate rapidly and have large tail currents. In the same patch, currents from a -40 mV holding potential are smaller, inactivate more slowly, and have practically no tail currents. 3. In cell-attached patches containing one of two L-type Ca2+ channels, currents from -80 or -40 mV are virtually identical, and they are similar to the currents from multichannel patches held at -40 mV. 4. The voltage-dependent, time-variant kinetics of individual L-type Ca2+ channels are unaltered if the patch is removed from the cell and forms an inside-out configuration. In these experiments the internal membrane was bathed with an artificial, intracellular-like solution containing no phosphorylating enzymes or substrates. 5. Cells bathed in 20 mM-Ba2+ solutions and held at -80 mV have currents with an early phase that inactivates in tens of milliseconds, a late phase that inactivates in hundreds of milliseconds, and a large, slow tail current. Currents from -40 mV have only the late phase and practically no tails. However, if the maximum current is less than 0.1 pA pF-1, records from either -80 or -40 mV are virtually identical, and they are similar to currents from cells with higher channel density held at -40 mV. Furthermore, if cells are stimulated before full recovery from inactivation, the reduced current is accompanied by slower inactivation. 6. Whole-cell currents in 1.5 mM-Ca2+ solutions are entirely abolished by addition of 20 microM-nifedipine, and they are enhanced 2-3 times by addition of 30 microM-cyclic AMP and 3 mM-ATP to the whole-cell recording electrode. The whole-cell currents in 20 mM-Ba2+ solutions are also completely blocked by 20 microM-nifedipine, regardless of kinetics or holding potential. Thus, by definition, the cells we are studying contain only L-type channels
Martensitic Thin Wires under Restrained Recovery: Theoretical and Experimental Aspects
A one-dimensional model for the evolution of microstructure in single crystal shape memory wires has been recently proposed in (Rizzoni (2011)). The model is based on the constrained theory of martensite introduced by (Ball et al. (1995); De Simone and James (2002)) and on the assumption that stable equilibrium configurations are deformations lying at the energy wells on most parts of the wire. In this paper we compare the response simulated for restrained recovery conditions (Rizzoni (2011)) with experimental data obtained in restrained recovery tests performed on NiTi wires. As an application, we consider a truss made of shape memory wires and rigid elements, and we calculate its deformation after thermal activation of the shape recovery
Thermal conductivity of clay bricks
In the present work the thermal conductivity of 29 samples of clay bricks was measured and the correlations of the thermal performance with the compositional, physical, and microstructural features of products were investigated. The results obtained directed our attention toward a better understanding of the role played by some parameters (i.e., mineralogical components and pore size distribution), other than bulk density, in improving or depressing the insulating properties of bricks. Among them, the unfavorable role of quartz, Ca-rich silicates, and amorphous phase came out, while the role of pore size and specific surface should be more accurately evaluated in the structural design of materials
PRIMI RISULTATI DI UN INDAGINE SULLO STATO DELLE SISTEMAZIONI IDRAULICO-FORESTALI NEL BACINO DELLâARNO
Il presente lavoro è relativo ai risultati ottenuti con il primo stato dâavanzamento di una ricerca sullo stato delle Sistemazioni Idraulico-Forestali per assegnate aree di indagine comprese nel bacino del fiume Arno affidata dallâ AutoritĂ di Bacino del Fiume Arno al Dipartimento di Ingegneria Agraria e Forestale dellâUniversitĂ degli Studi di Firenze.
Innanzi tutto, è stata condotta unâanalisi preventiva, mediante un database, di documentazione relativa alle opere idrauliche giĂ censite in precedenti lavori (prof. Grazi) con identificazione della posizione geografica delle opere stesse con lâausilio di software GIS. A questa prima fase sono seguiti la predisposizione di una opportuna scheda di rilievo (sia cartacea sia elettronica) e quindi sopralluoghi in campo condotti mediante lâausilio di un GPS collegato a computer palmare per il supporto cartografico di base. Rilievi di dettaglio sono stati condotti nei torrenti dellâarea del Mugello, giĂ oggetto di studi risalenti a una trentina di anni fa per la valutazione delle pendenze di compensazione (Falciai et al.) che sono stati utilizzati spesso in letteratura (Ferro et al., Pica et al., etc.). Con riferimento ad altre zone campione del bacino (es. Casentino e Area Fiorentina), la documentazione storica ed il sopralluogo in campo (su base statistica) ha avuto lo scopo di rintracciare le opere esistenti e verificare lâattendibilitĂ e la confrontabilitĂ dei vari censimenti eseguiti anche da altri Enti preposti. In particolare si è analizzato il dimensionamento delle opere ed il loro stato attuale di conservazione ed efficienza, confrontandolo con quanto riportato in eventuali elaborati progettuali e nei censimenti precedenti. Eventuali danneggiamenti dei manufatti possono essere derivati dalle valutazioni in sede progettuale, da scarsa o inesistente manutenzione o da mutate caratteristiche in alveo e nel bacino. Per avere qualche indicazione in proposito si è valutata la portata di progetto a partire dalle dimensioni delle gavete considerate come stramazzi in parete grossa e se ne è stimato il tempo di ritorno, mediante i modelli AlTo (Regione Toscana) e Idrarno (AutoritĂ di Bacino). Questa fase ha richiesto un lavoro preventivo di queries spaziali che hanno lo scopo di attribuire il codice dellâasta a cui appartengono le opere idrauliche in esame (allâinterno del reticolo idrografico del modello AlTo e allâinterno del reticolo âSistema Acqueâ dellâAutoritĂ di Bacino dellâArno). Questa operazione consente, inoltre, il collegamento tra il contenuto informativo del geodatabase dellâAutoritĂ di Bacino con il sistema di regionalizzazione delle portate di piena della Regione Toscana. Mediante la misura delle caratteristiche dimensionali dellâopera si sono cercate di ricavare anche indicazioni statistiche riguardo alla pendenza di compensazione dei corsi dâacqua in esame.
Le verifiche in campo ha permesso anche una descrizione delle condizioni generali dellâalveo in cui sono situate le opere e dei versanti siti in prossimitĂ delle opere stesse. I dati raccolti sono stati immessi in un geodatabase opportunamente costruito secondo lo standard di quello esistente presso lâAutoritĂ di Bacino del Fiume Arno e quindi elaborati per la ricerca delle relazioni tra le caratteristiche delle opere e la pendenza attuale dellâalveo nonchĂŠ la stima della necessitĂ , per i corsi dâacqua esaminati, di opere atte a garantire la continuitĂ fluviale per la ittiofauna (Pini Prato e Barneschi)
Equilibrium moisture content of clay bricks: The influence of the porous structure
The comprehension of the influence exerted by the material microstructure on the hygrometric properties of clay bricks plays a fundamental role in order to control the condensation phenomena and to avoid the deterioration of the masonry structure. The equilibrium moisture content (MEq) of ordinary and lightweight clay bricks was measured and the correlation with microstructure and pore morphology was investigated. The influence of the pore size and specific surface on the amount of MEq was found to be prevalent when compared to the other physical variables. A statistical model was also set up in order to predict the MEq values
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